The present invention relates to high pressure, fluid drilling of rock.
It is known that rock can be drilled by fluid at extremely high pressure. The fluid erodes the rock away. These fluid drills operate at pressures of the order of 5,000 Kg/cm.sup.2 with a jet velocity of the order of 200 to 1,000 m/sec.
Proposed techniques for exploiting this technique of rock penetration in petroleum well formation have recognized and sought to use the high total head of drilling mud available in the zone where rock erosion is to take place. The head can represent several thousands of meters of dense drilling mud. These techniques have also recognized the use of drilling mud to clear out rock chips formed during rock erosion.
U.S. Pat. No. 3,112,800 to Bobo describes a downwell drilling technique. This patent describes a fluid-operated motor and pump near the bottom of a well. The pump provides high pressure fluid discharged as a jet to erode rock in the bore hole. The pump described in the Bobo patent is a reciprocating pump of the piston type.
Downhole turbines have also been used in drilling. Thus a power turbine has been used to drive a drill bit. An example of this is U.S. Pat. No. 2,908,534 to Rietsch.
Drilling mud is a dense fluid used to seal formation fluids in the ground and prevent them from blowing out the well. Drilling mud contains solids which erode pump and turbine parts. To use drilling mud also as a working and power fluid for downhole equipment requires that the solids of the mud be removed.